Metal oxide semiconductor field-effect transistor (mosfet) devices and manufacturing methods thereof

ABSTRACT

Provided are metal oxide field-effect transistor (MOSFET) devices having a metal gate structure, in which a work function of the metal gate structure is uniform along a length direction of a channel, and manufacturing methods thereof. The MOSFET devices include a semiconductor substrate, an active area on the semiconductor substrate and extending in a first direction, and a gate structure on the semiconductor substrate. The gate structure extends across the active area in a second direction that traverses the first direction and comprises a high-k layer, a first metal layer, a work function control (WFC) layer, and a second metal layer, which are sequentially stacked on the active area. A lower surface of the WFC layer may be longer than a first interface between a lower surface of the first metal layer and an upper surface of the high-k layer in the first direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 U.S.C. § 119to Korean Patent Applications No. 10-2020-0051817, filed on Apr. 28,2020, and 10-2020-0115517, filed on Sep. 9, 2020, in the KoreanIntellectual Property Office, the disclosures of which are incorporatedby reference herein in their entireties.

BACKGROUND

The inventive concept relates to metal oxide semiconductor field-effecttransistor (MOSFET) devices, and more particularly, to MOSFET devicesincluding a metal gate structure and manufacturing methods of the MOSFETdevices.

Due to the development of electronics technology, down-scaling ofsemiconductor devices has recently progressed rapidly. Recently, becauseof demand for semiconductor devices to perform at a high speed and toperform accurate operations, various studies have been conducted forimproving a structure of a transistor included in a semiconductordevice, for example, a MOSFET.

SUMMARY

The inventive concept provides metal oxide semiconductor field-effecttransistor (MOSFET) devices having a metal gate structure, in which awork function of the metal gate structure is uniform along a lengthdirection of a channel, and manufacturing methods thereof.

According to some embodiments of the inventive concept, there areprovided metal oxide field-effect transistor (MOSFET) devices,including: a semiconductor substrate; an active area on thesemiconductor substrate and extending in a first direction; and a gatestructure on the semiconductor substrate, the gate structure extendingacross the active area in a second direction that traverses the firstdirection and comprising an interface layer, a high-k layer, a firstmetal layer, a work function control (WFC) layer, and a second metallayer, which are sequentially stacked on the active area, and each ofthe high-k layer, the first metal layer, the WFC layer, and the secondmetal layer comprising a lower surface facing the semiconductorsubstrate and an upper surface opposite the lower surface, wherein thelower surface of the WFC layer is longer than a first interface betweenthe lower surface of the first metal layer and the upper surface of thehigh-k layer in the first direction.

According to some embodiments of the inventive concept, there areprovided MOSFET devices, including: a semiconductor substrate; an activearea protruding from the semiconductor substrate and extending in afirst direction; a gate structure on the semiconductor substrate, thegate structure extending in a second direction that traverses the firstdirection and covering at least a portion of the active area, the gatestructure comprising an interface layer, a high-k layer, a first metallayer, a WFC layer, and a second metal layer, which are sequentiallystacked on the active area, and each of the high-k layer, the firstmetal layer, the work function control (WFC) layer, and the second metallayer comprising a lower surface facing the semiconductor substrate andan upper surface opposite the lower surface; and source and drain areasrespectively on side surfaces of the gate structure, the side surfacesof the gate structure being spaced apart from each other in the firstdirection, wherein the lower surface of the WFC layer is longer than afirst interface between the lower surface of the first metal layer andthe upper surface of the high-k layer in the first direction.

According to some embodiments of the inventive concept, there areprovided manufacturing methods MOSFET device, the manufacturing methodincluding: forming an active area having a fin shape, protruding from asemiconductor substrate and extending in a first direction; forming, onthe semiconductor substrate, a dummy gate structure extending in asecond direction that traverses the first direction and covering aportion of the active area; forming two spacers respectively on sidesurfaces of the dummy gate structure, the side surfaces of the dummygate structure being spaced apart from each other in the firstdirection; removing the dummy gate structure between the two spacers;forming a high-k layer between the two spacers; etching inner sidesurfaces of the two spacers to increase distance between the twospacers; forming a first metal layer on an upper surface of the high-klayer; forming a WFC layer on the first metal layer; and forming asecond metal layer on the WFC layer, wherein a lower surface of the WFClayer is longer than a first interface between a lower surface of thefirst metal layer and the upper surface of the high-k layer in the firstdirection.

According to some embodiments of the inventive concept, there areprovided manufacturing methods of a MOSFET device, the manufacturingmethod including: forming an active area having a fin shape, protrudingfrom a semiconductor substrate and extending in a first direction;forming, on the semiconductor substrate, a dummy gate structureextending in a second direction that traverses the first direction andcovering a portion of the active region; forming two spacersrespectively on side surfaces of the dummy gate structure, the sidesurfaces of the dummy gate structure being spaced apart from each otherin the first direction; removing the dummy gate structure between thetwo spacers; conformally forming a high-k layer between the two spacers,the high-k layer comprising protruding portions extending respectivelyon inner side surfaces of the two spacers; conformally forming a firstmetal layer on the high-k layer, the first metal layer comprisingprotruding portions extending respectively on the inner side surfaces ofthe two spacers; removing the protruding portions of the high-k layerand the first metal layer; conformally forming a WFC layer on the high-klayer, the first metal layer, and the two spacers; and conformallyforming a second metal layer on the WFC layer, wherein a lower surfaceof the WFC layer is longer than a first interface between a lowersurface of the first metal layer and an upper surface of the high-klayer in the first direction.

According to some embodiments of the inventive concept, there areprovided metal oxide field-effect transistor (MOSFET) devices,including: a substrate; an active area on the substrate; a gatestructure on the active area, the gate structure comprising a high-klayer, a first metal layer, a work function control (WFC) layer, and asecond metal layer that are sequentially stacked on the active area, andeach of the high-k layer, the first metal layer, the WFC layer, and thesecond metal layer comprising a lower surface facing the active area andan upper surface opposite the lower surface; and source/drain regionsrespectively adjacent side surfaces of the gate structure. The lowersurface of the WFC layer may protrude outwardly beyond opposing ends ofan interface between the lower surface of the first metal layer and theupper surface of the high-k layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments of the inventive concept will be more clearlyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is a perspective view and FIGS. 2A, 2B, and 2C arecross-sectional views of a metal oxide semiconductor field-effecttransistor (MOSFET) device according to some embodiments of theinventive concept;

FIG. 3 is a conceptual diagram illustrating diffusion paths of a workfunction control (WFC) material in a gate structure of the MOSFET deviceof FIG. 1;

FIGS. 4A and 4B are simulation pictures respectively showing aconcentration of a WFC material on an interface between a highdielectric layer and a first metal layer in a first comparative MOSFETdevice and the MOSFET device of FIG. 1;

FIG. 5 is a graph showing work functions of each portion of a gatestructure of the first comparative MOSFET device and the MOSFET of FIG.1;

FIGS. 6A and 6B are cross-sectional views of a MOSFET device accordingto some embodiments of the inventive concept;

FIG. 7 is a conceptual diagram illustrating diffusion paths of a WFCmaterial in a gate structure of the MOSFET device of FIG. 6A;

FIG. 8 is a graph showing work functions of each portion of a gatestructure of a second comparative MOSFET device and the MOSFET device ofFIG. 6A;

FIGS. 9A to 9D are cross-sectional views of a MOSFET device according tosome embodiments of the inventive concept;

FIGS. 10A and 10B are cross-sectional views of a MOSFET device accordingto some embodiments of the inventive concept;

FIGS. 11A and 11B are cross-sectional views of a MOSFET device accordingto some embodiments of the inventive concept;

FIGS. 12A to 12H are cross-sectional views schematically illustrating amethod of manufacturing the MOSFET device of FIG. 1, according to someembodiments of the inventive concept;

FIGS. 13A and 13B are cross-sectional views schematically illustrating amethod of manufacturing the MOSFET device of FIG. 1, according to someembodiments of the inventive concept;

FIGS. 14A to 14E are cross-sectional views schematically illustrating amethod of manufacturing the MOSFET device of FIG. 6A, according to someembodiments of the inventive concept; and

FIGS. 15A to 15B are cross-sectional views schematically illustrating amethod of manufacturing the MOSFET device of FIG. 9D, according to someembodiments of the inventive concept.

DETAILED DESCRIPTION

Hereinafter, the inventive concept will be described in detail byexplaining example embodiments of the inventive concept with referenceto the attached drawings. Like reference numerals denote like elementsin different drawings, and redundant descriptions thereof may beomitted.

FIG. 1 is a perspective view and FIGS. 2A to 2C are cross-sectionalviews of a metal oxide semiconductor field-effect transistor (MOSFET)device 100 according to some embodiments of the inventive concept,wherein FIG. 2A is a horizontal cross-sectional view of the MOSFETdevice 100, taken along line I-I′, and FIGS. 2B and 2C are verticalcross-sectional views of the MOSFET device 100, respectively taken alonglines II-II′ and III-III′.

Referring to FIGS. 1 to 2C, the MOSFET device 100 may include asemiconductor substrate 101, an active area ACT (hereinafter, referredto as “fin active area”) of a fin F structure, and a gate structure 120.

The semiconductor substrate 101 may be or may include, for example, asilicon bulk wafer or a silicon-on-insulator (SOI) wafer. A material ofthe semiconductor substrate 101 is not limited to silicon. For example,the semiconductor substrate 101 may include a Group IV semiconductorsuch as germanium (Ge), a Group IV-IV compound semiconductor such assilicon-germanium (SiGe), silicon carbide (SiC), or the like, or a GroupIII-V compound semiconductor such as gallium arsenide (GaAs), indiumarsenide (InAs), indium phosphide (InP), or the like. In someembodiments, the semiconductor substrate 101 may be or may include aSiGe wafer, an epitaxial wafer, a polished wafer, an annealed wafer, orthe like. The semiconductor substrate 101 may be a p-type substrateincluding p-type impurity ions or an n-type substrate including n-typeimpurity ions. For example, in the MOSFET device 100 of the presentembodiment, the semiconductor substrate 101 may be a p-type substrate.

The fin active area ACT may have a structure protruding from thesemiconductor substrate 101 and extending in a first direction (anx-direction). A plurality of fin active areas ACT may be arranged on thesemiconductor substrate 101 to be apart from each other in a seconddirection (a y-direction). The second direction (the y-direction) maytraverse the first direction (the x-direction). In some embodiments, thesecond direction may be perpendicular to the first direction. Theplurality of fin active areas ACT may be electrically insulated fromeach other through a device isolation film 110 or the like. As usedherein, “an element A extends in a direction X” (or similar language)may mean that the element A extends longitudinally in the direction X.

Each of the plurality of fin active areas ACT may include a fin 105 andsource/drain areas 103. The fin 105 may include a lower fin portion 105d, in which both side surfaces thereof are surrounded by the deviceisolation film 110, and an upper fin portion 105 u protruding from anupper surface of the device isolation film 110. The upper fin portion105 u may be arranged below the gate structure 120 and may form achannel area. The source/drain areas 103 may be arranged on respectiveside surfaces of the gate structure 120 in the first direction (thex-direction) and may be arranged on the lower fin portion 105 d.

The fin 105 may be formed based on the semiconductor substrate 101. Inaddition, the source/drain areas 103 may be formed through an epitaxialfilm growth by using the lower fin portion 105 d as a seed. According tosome embodiments, the upper fin portion 105 u may also form thesource/drain areas 103 on respective side surfaces of the gate structure120. For example, the source/drain areas 103 may not be formed through aseparate epitaxial film growth, but may be formed by the upper finportion 105 u of the fin 105.

When the fin 105 is formed based on the semiconductor substrate 101, thefin 105 may include silicon or germanium, which are semiconductorelements. In addition, the fin 105 may include a compound semiconductorsuch as a Group IV-IV compound semiconductor or a Group III-V compoundsemiconductor. For example, the fin 105 may, as the Group IV-IV compoundsemiconductor, include a binary compound, a ternary compound, whichincludes at least two of carbon (C), silicon (Si), germanium (Ge), andtin (Sn), or a compound in which a Group IV element is doped with thebinary compound and the ternary compound. In addition, for example, thefin 105 may, as the Group III-V compound semiconductor, include at leastone of a binary compound, a ternary compound, and a quaternary compound,which are formed by combining at least one of aluminum (Al), gallium(Ga), and indium (In) as Group III elements and one of phosphorus (P),arsenic (As), and antimony (Sb) as Group V elements.

The source/drain areas 103 may be formed on respective side surfaces ofthe gate structure 120 and on the lower fin portion 105 d and mayinclude a compressive stress material or a tensile stress materialaccording to a channel type of a transistor (e.g., a conductivity typeof a transistor). For example, when the MOSFET device 100 forms a p-typemetal oxide semiconductor (PMOS), the source/drain areas 103 on bothside surfaces of the gate structure 120 may include a compressive stressmaterial. In detail, when the lower fin portion 105 d includes silicon,the source/drain areas 103 may, as a compressive stress material,include a material having a greater lattice constant than that ofsilicon, for example, silicon germanium (SiGe). In addition, when theMOSFET device 100 forms a NMOS, the source/drain areas 103 on both sidesurfaces of the gate structure 120 may include a tensile stressmaterial. In detail, when the lower fin portion 105 d includes silicon,the source/drain areas 103 may, as a tensile stress material, includesilicon or a material having a lower lattice constant than that ofsilicon, for example, silicon carbide (SiC).

In the MOSFET device 100 of the present embodiment, the source/drainareas 103 may have various shapes. For example, when viewing the MOSFETdevice 100 in a shape of a cross-section perpendicular to the firstdirection (the x-direction), the source/drain areas 103 may have a shapesuch as a diamond, a circle, an ellipse, a polygon, a trapezoid, or thelike. In FIG. 1, the source/drain area 103 is illustrated in a hexagonaldiamond shape as an example.

The device isolation film 110 may be arranged on the semiconductorsubstrate 101. As shown in FIG. 2C, the device isolation film 110 may bearranged to cover both side surfaces of the lower fin portion 105 d ofthe fin 105, which are spaced apart from each other in the seconddirection (the y-direction). The device isolation film 110 mayelectrically separate fins 105 arranged in the second direction (they-direction). The device isolation film 110 may include, for example, atleast one of a silicon oxide film, a silicon nitride film, a siliconoxynitride film, and a combination thereof. The upper fin portion 105 uof the fin 105 may not be surrounded by the device isolation film 110and may have a structure protruding from the upper surface of the deviceisolation film 110. In addition, as shown in FIGS. 2B and 2C, the upperfin portion 105 u of the fin 105 may be arranged below the gatestructure 120 and may form a channel area. As used herein, “an element Acovers an element B” (or similar language) means that the element A ison and overlaps the element B but does not necessarily mean that theelement A covers the element B entirely.

The gate structure 120 may cross the fin 105 on the device isolationfilm 110 and extend in the second direction (the y-direction). Aplurality of gate structures 120 may be arranged with respect to one fin105. For example, the plurality of gate structures 120 may traverse asingle fin 105. In addition, the plurality of gate structures 120 may bearranged to be spaced apart from each other in the first direction (thex-direction). Each of the plurality of gate structures 120 may be formedin a structure covering an upper surface of the upper fin portion 105 uof the fin 105 and both side surfaces of the upper fin portion 105 u.

Each of the plurality of gate structures 120 may include an interfacelayer 121, a high dielectric layer 123, a first metal layer 125, a workfunction control (WFC) layer 127, and a second metal layer 129.

The interface layer 121 may be formed above the semiconductor substrate101 and may include an insulating material such as an oxide film, anitride film, or an oxynitride film. For example, the interface layer121 may include silicon oxide (SiO₂) or silicon oxynitride (SiON). Theinterface layer 121 may form a gate oxide film together with the highdielectric layer 123.

The high dielectric layer 123 is also referred to as a high-k layer, andmay include a dielectric material having a high dielectric constant (k).The high dielectric layer 123 may include a hafnium-based (Hf-based)material or a zirconium-based (Zr-based) material. For example, the highdielectric layer 123 may include hafnium oxide (HfO₂), hafnium siliconoxide (HfSiO), hafnium silicon oxynitride (HfSiON), hafnium oxynitride(HfON), hafnium aluminum oxide (HfAlO), hafnium lanthanum oxide (HfLaO),zirconium oxide (ZrO₂), zirconium silicon oxide (ZrSiO), or the like.

In some embodiments, the high dielectric layer 123 is not limited to aHf-based material or a Zr-based material, and may include othermaterials, such as lanthanum oxide (La₂O₃), lanthanum aluminum oxide(LaAlO₃), tantalum oxide (Ta₂O₅), titanium oxide (TiO₂), strontiumtitanium oxide (SrTiO₃), yttrium oxide (Y₂O₃), aluminum oxide (Al₂O₃),lead scandium tantalum oxide (PbSc_(0.5)Ta_(0.5)O₃), lead zinc niobate(PbZnNbO₃), or the like.

The high dielectric layer 123 may be formed to have a thickness ofseveral nanometers (nm) through various deposition methods such asatomic layer deposition (ALD), chemical vapor deposition (CDC), physicalvapor deposition (PVD), or the like. However, the thickness of the highdielectric layer 123 is not limited to the above value. To adjust adiffusion amount of a WFC material from the WFC layer 127, a filmstructure, the thickness, or the like of the high dielectric layer 123may be adjusted when forming the high dielectric layer 123. In addition,according to some embodiments, a heat treatment may be performed on thehigh dielectric layer 123.

The first metal layer 125 may be arranged on the high dielectric layer123. The first metal layer 125 may include, for example, a nitride oftitanium (Ti), a nitride of tantalum (Ta), an oxynitride of Ti, or anoxynitride of Ta. For example, the first metal layer 125 may include abielement metal nitride such as titanium nitride (TiN), tantalum nitride(TaN), or the like, a tri-element metal nitride such as titaniumaluminum nitride (TiAlN), tantalum aluminum nitride (TaAlN), titaniumsilicon nitride (TiSiN), or the like, or a form in which the metalnitrides are oxidized, that is, a metal oxynitride.

The first metal layer 125 may be formed to have a thickness of severalnanometers (nm) through various deposition methods such as ALD, CVD,PVD, or the like. However, the thickness of the first metal layer 125 isnot limited to the above value. To adjust a diffusion amount of the WFCmaterial from the WFC layer to an interface between the first metallayer 125 and the high dielectric layer 123, when forming the firstmetal layer 125, a film structure, a composition of metal, thethickness, an operation temperature, operation time, or the like thereofmay be adjusted. In addition, according to some embodiments, a heattreatment may be performed on the first metal layer 125.

The first metal layer 125 may form a metal electrode of the gatestructure 120 together with the second metal layer 129 above the firstmetal layer 125. The first metal layer 125 may include a metal havingcertain work functions, and in addition, may assist a function ofadjusting work functions of the WFC layer 127 by adjusting the diffusionamount of the WFC material from the WFC layer 127 to the interface ofthe first metal layer 125 and the high dielectric layer 123.

The WFC layer 127 may include the WFC material. For example, the WFCmaterial of the WFC layer 127 may be Al. The WFC material of the WFClayer 127 is not limited to Al. In the MOSFET device 100 of the presentembodiment, the WFC layer 127 may include, for example, titaniumaluminum carbide (TiAlC) or titanium aluminum nitride (TiAlN). Amaterial of the WFC layer 127 is not limited to the above materials.

The WFC layer 127 may supply the WFC material, for example, Al, to theinterface (see Is1 of FIG. 3, hereinafter, simply referred to as “firstinterface”) of the high dielectric layer 123 and the first metal layer125 through diffusion. Herein, the first interface Is1 is not an entireinterface in which the high dielectric layer 123 and the first metallayer 125 are in contact and may be defined as only a lower surfaceportion of a lower surface of the first metal layer 125, the lowersurface portion being in contact with an upper surface of the highdielectric layer 123. The first interface Is1 will be described in moredetail below in the descriptions of FIGS. 3 and 7.

Depending on an amount of the WFC material supplied to the firstinterface Is1 through diffusion, a work function or a threshold voltageof the gate structure 120 may be changed. For example, the workfunctions of the gate structure 120 may decrease as a concentration ofthe WFC material on the first interface Is1 increases. However, theinventive concept is not limited thereto. According to some embodiments,the work functions of the gate structure 120 may also increase as theconcentration of the WFC material on the first interface Is1 increases.

The work functions of the gate structure 120 may not uniformly changethroughout the gate structure 120 according to the concentration of theWFC material on the first interface Is1. In other words, in the workfunctions of the gate structure 120, a work function of a correspondingportion of the gate structure 120 may be changed according to theconcentration of the WFC material at each position of the firstinterface Is1. For example, a work function of a portion of the gatestructure 120 may depend on and may vary according to a concentration ofthe WFC material on a portion of the first interface Is1, which isincluded in the portion of the gate structure 120. In detail, when thefirst direction (the x-direction) is a length direction of the gatestructure 120 or a length direction of a channel, and the gate structure120 is divided into a gate center and a gate edge of both outer edges ofthe gate structure 120 in the first direction (the x-direction), theconcentration of the WFC material of a center portion of the firstinterface Is1 corresponding to the gate center of the gate structure 120may be high, and the concentration of the WFC material of an edgeportion of the first interface Is1 corresponding to the gate edge of thegate structure 120 may be low. In this case, a work function of the gateedge of the gate structure 120 may be greater than a work function ofthe gate center of the gate structure 120. This phenomenon, in which, inthe length direction of the gate structure 120, the concentration of theWFC material is lower at the edge portion than at the center portion ofthe first interface Is1, such that the work function of the gate edge ofthe gate structure 120 becomes greater than that of the gate centerthereof, is referred to as a gate work function roll-up (GWR)phenomenon.

The second metal layer 129 may be formed on the WFC layer 127 and mayinclude an n-type metal or a p-type metal. For reference, the n-typemetal may refer to a metal forming a gate electrode of an n-type metaloxide semiconductor (NMOS), and the p-type metal may refer to a metalforming a gate electrode of a PMOS. When the second metal layer 129includes the n-type metal, the second metal layer 129 may include Ti orTa. For example, the second metal layer 129 may include a metal materialsuch as TiN, TiAlN, titanium aluminum carbonitride (TiAlC—N), titaniumaluminum (TiAl), TaN, TaAlN, tantalum aluminum carbonitride (TaAlC—N),tantalum aluminum (TaAl), or the like. A material of the second metallayer 129, as the n-type metal, is not limited to the above materials.In addition, the second metal layer 129, as the n-type metal, mayinclude a single layer or a multi-layer. When the second metal layer 129includes a p-type metal, the second metal layer 129 may include at leastone of molybdenum (Mo), palladium (Pd), ruthenium (Ru), platinum (Pt),TiN, tungsten nitride (WN), TaN, iridium (Ir), tantalum carbide (TaC),ruthenium nitride (RuN), and molybdenum nitride (MoN). The material ofthe second metal layer 129, as the p-type metal, is not limited to theabove materials. In addition, the second metal layer 129, as the p-typemetal, may include a single layer or a multi-layer.

According to some embodiments, the gate structure 120 may furtherinclude a gap-fill metal layer. A structure including the gap-fill metallayer will be described in more detail below in the descriptions ofFIGS. 10A and 10B.

Spacers 130 may be arranged on both side surfaces of the gate structure120, which are spaced apart from each other in the first direction (thex-direction). In addition, like the gate structure 120, the spacers 130may have a structure extending in the second direction (they-direction). Accordingly, similar to the gate structure 120, thespacers 130 may have a structure crossing the fin 105 and surroundingthe upper surface of the upper fin portion 105 u of the fin 105.

As shown in FIGS. 2A and 2B, each of the spacers 130 may have a step inan inner side surface thereof. That is, the inner side surface of thespacer 130 is in contact with the side surface of the gate structure120, and because the interface layer 121 and the high dielectric layer123 of the gate structure 120 are shorter than the first metal layer125, the WFC layer 127, and the second metal layer 129 in the firstdirection (the x-direction), inner side surface portions of the spacers130 corresponding to the interface layer 121 and the high dielectriclayer 123 may have an inward structure. Accordingly, the inner sidesurfaces of the spacers 130 may have steps at a boundary portion of thehigh dielectric layer 123 and the first metal layer 125.

The spacers 130 may include an insulating material such as a nitridefilm or an oxynitride film. For example, the spacers 130 may include asilicon nitride film or a silicon oxynitride film. The spacers 130 mayinclude a single layer or a multi-layer.

Although not illustrated in the drawings, an interlayer insulating filmmay be arranged on the device isolation film 110 to cover thesource/drain areas 103. For example, the interlayer insulating film mayhave a structure surrounding upper and side surfaces of the source/drainareas 103 and also surrounding side surfaces of the spacers 130.

In the MOSFET device 100 of the present embodiment, an interface betweenthe WFC layer 127 and the first metal layer 125 (see Is2 of FIG. 3,hereinafter, simply referred to as “second interface”) is formed longerthan the first interface Is1 in the length direction of the channel,that is, the first direction (the x-direction) in which the fin 105extends, such that concentrations of the WFC material on the firstinterface Is1 may be uniform (e.g., uniform along the length directionof the channel), and the GWR phenomenon of the gate structure 120 may besuppressed. Accordingly, the MOSFET device 100 of the present embodimentenables a reliable MOSFET device having a uniform work function of agate structure in a length direction of a channel. Herein, the secondinterface Is2 may be defined as a portion in which a lower surface ofthe WFC layer 127 contacts a layer thereunder (e.g., the first metallayer 125), and may be substantially the same as the lower surface ofthe WFC layer 127. The second interface Is2 and the GWR phenomenon willbe described in more detail below in the descriptions of FIGS. 3 to 5,7, and 8.

FIG. 3 is a conceptual diagram illustrating diffusion paths of the WFCmaterial in the gate structure 120 of the MOSFET device 100 of FIG. 1and may correspond to a portion of the gate structure 120 of FIGS. 2Aand 2B.

Referring to FIG. 3, in the MOSFET device 100 of the present embodiment,the first interface Is1 may be defined as only a lower surface portionof the lower surface of the first metal layer 125, the lower surfaceportion being in contact with the upper surface of the high dielectriclayer 123, and the second interface Is2 may be defined as a portion inwhich the lower surface of the WFC layer 127 contacts a layerthereunder. The first interface Is1 may be defined as a portion of asurface of the first metal layer 125, which directly contacts the highdielectric layer 123. Based on this definition, in FIG. 3, the firstinterface Is1 may have a first length L1 in the first direction (thex-direction), and the second interface Is2 may have a second length L2in the first direction (the x-direction). The second length L2 may begreater than the first length L1. The second length L2 may be greaterthan the first length L1 by lengths of two small double-headed arrows atopposing sides of the high dielectric layer 123, which are spaced partfrom each other in the first direction (the x-direction). In someembodiments, the lower surface of the WFC layer 127 may protrudeoutwardly beyond opposing ends of the first interface Is1 as illustratedin FIG. 3. In some embodiments, portions of the lower surface of the WFClayer 127 that protrude beyond the respective opposing ends of the firstinterface Is1 have an equal length in the first direction (thex-direction).

In view of the diffusion paths of the WFC material of the WFC layer 127,the WFC material (for example, Al) may move from the second interfaceIs2 of the WFC layer 127 to the first interface Is1 in a third direction(a z-direction) or the second direction (the y-direction). In addition,as illustrated by small single-headed arrows, paths through which theWFC material diffuses from the second interface Is2 to each portion ofthe first interface Is1 may be substantially the same as each other in acenter portion and an edge portion of the first metal layer 125.Accordingly, in the MOSFET device 100 of the present embodiment, theconcentration of the WFC material at the center portion of the firstinterface Is1 may be substantially the same as the concentration of theWFC material at the edge portion of the first interface Is1 in the firstdirection (the x-direction). In other words, the concentrations of theWFC material on the first interface Is1 along the first direction (thex-direction) may be uniform, and accordingly, the GWR phenomenon may notoccur in the gate structure 120 or may be greatly improved.

As illustrated in FIG. 3, numbers of diffusion paths through which theWFC material diffuses from the second interface Is2 or the WFC layer 127to the center portion and the edge portion of the first interface Is1may be substantially equal to each other, and thus the concentrations ofthe WFC material in the center portion and the edge portion of the firstinterface Is1 may be substantially equal to each other. In contrast,when a first MOSFET device (also referred to as a first comparativeMOSFET device) includes the first interface Is1 and the second interfaceIs2 that have equal lengths in the first direction (the x-direction),diffusion paths represented by bold arrows in FIG. 3 may not exist.Therefore, the concentration of the WFC material at the edge portion ofthe first interface Is1 may be lower than that at the center portion ofthe first interface Is1, and the GWR phenomenon may be caused by thedifference in the concentrations of the WFC material on the firstinterface Is1.

FIGS. 4A and 4B are simulation pictures respectively showing aconcentration of a WFC material on a first interface between a highdielectric layer and a first metal layer in the first comparative MOSFETdevice and the MOSFET device of FIG. 1.

Referring to FIG. 4A, the first comparative MOSFET device may have ahigh concentration of the WFC material in the center portion of thefirst interface of the gate center of the gate structure 120 and mayhave a low concentration of the WFC material in the edge portion of thefirst interface of the gate edges of the gate structure 120. The firstinterface is enclosed by the dotted line in the FIG. 4A. For reference,the darker the first interface, the higher the concentration of the WFCmaterial, and the lighter the first interface, the lower theconcentration of the WFC material.

On the other hand, the MOSFET device 100 of the present embodiment ofFIG. 4B may have a concentration of the WFC material in the centerportion of the first interface of the gate center of the gate structure120 that is substantially equal to a concentration of the WFC materialin the edge portion of the first interface of the gate edges of the gatestructure 120. Although there are some bright portions in the lowersurface of the first metal layer 125 of the gate edges, because thebright portions are not included on the first interface and do notcorrespond to a channel area, the bright portions are not related to anadjustment of (e.g., may not affect) the work function of the gatestructure 120 or the GWR phenomenon.

FIG. 5 is a graph showing work functions in each portion of the gatestructure 120 of the first comparative MOSFET device and the MOSFETdevice 100 of FIG. 1, wherein a solid line represents work functions ofthe first comparative MOSFET device, and a dashed line represents workfunctions of the MOSFET device 100 of FIG. 1. The x-axis represents aposition in the gate structure 120, the y-axis represents workfunctions, and a unit may be an arbitrary unit.

Referring to FIG. 5, regarding the GWR phenomenon in which the workfunction of the gate edge of the gate structure 120 is greater than thework function of the gate center of the gate structure 120, a differencein work functions between the gate center and the gate edge is a firstGWR GWR1 in the first comparative MOSFET device, and is a second GWRGWR2 in the MOSFET device 100 of the present embodiment. The first GWRGWR1 may be relatively large, for example, about 100 meV. On the otherhand, the second GWR GWR2 may be very small, for example, less than 10meV, and in addition, according to some embodiments, the second GWR GWR2may decrease to almost zero. In some embodiments, the second GWR GWR2may be about zero. When the work function of the gate center is about4.5 eV, the first GWR GWR1 is about 2.25% of the work function of thegate center, which is greater than 1% of the work function of the gatecenter, and the second GWR GWR2 may be about 0.2% of the work functionof the gate center, which is less than 1% of the work function of thegate center. In other words, in the MOSFET device 100 of the presentembodiment, the GWR may be reduced to 1/10 or less compared to that ofthe first comparative MOSFET device.

When the GWR phenomenon is reduced, the controllability of the gatestructure 120 may be improved, and direct current (DC) performance ofthe MOSFET device 100 may be improved. Herein, the DC performance maymean, for example, off-current performance, and when the off-currentperformance is good, little current flows below an operating voltage,and leakage may be minimized. The DC performance is not limited to theoff-current performance. For example, in the MOSFET device 100 accordingto the present embodiment, the DC performance may be improved by 2% ormore as compared to that of the first comparative MOSFET device.

The MOSFET device 100 of the present embodiment may include the gatestructure 120 having a structure in which the second interface Is2 islonger than the first interface Is1 in the first direction (thex-direction), which is the length direction of the channel, such thatthe concentrations of the WFC material on the first interface Is1 may beuniform (e.g., uniform along the first direction (the x-direction)), andthe work functions of the gate structure 120 may be uniform (e.g.,uniform along the first direction (the x-direction)). Accordingly, theMOSFET device 100 of the present embodiment reduces the GWR phenomenonof the gate structure 120 to almost zero, thereby implementing areliable MOSFET device.

FIGS. 6A and 6B are cross-sectional views of a MOSFET device 100 aaccording to some embodiments of the inventive concept, which correspondto FIGS. 2A and 2B, and a cross-sectional view of the MOSFET device 100a corresponding to FIG. 2C is substantially the same as FIG. 2C and thuswill be omitted. Descriptions already given with respect to FIGS. 1 to2C are briefly given or omitted below.

Referring to FIGS. 6A and 6B, the MOSFET device 100 a of the presentembodiment may be different from the MOSFET device 100 of FIG. 1 in astructure of a gate structure 120 a. In detail, in the MOSFET device 100a of the present embodiment, a high dielectric layer 123 a may have aU-shape covering a lower surface of a first metal layer 125 a and bothside surfaces of the first metal layer 125 a, which are spaced apartfrom each other in the first direction (the x-direction). Due to theU-shape of the high dielectric layer 123 a, an upper surface of thefirst metal layer 125 a and upper surfaces of protruding portions onboth sides of the high dielectric layer 123 a may be on substantiallythe same plane and may be in contact with a lower surface of a WFC layer127 a.

In addition, the WFC layer 127 a may have a U-shape covering a lowersurface of a second metal layer 129 a and both side surfaces of thesecond metal layer 129 a, which are spaced apart from each other in thefirst direction (the x-direction). Due to the U-shape of the WFC layer127 a, an upper surface of the second metal layer 129 a, upper surfacesof protruding portions on both sides of the WFC layer 127 a, and uppersurfaces of spacers 130 a may be on substantially the same plane.

Side surfaces of an interface layer 121 a, the high dielectric layer 123a, and the WFC layer 127 a may form side surfaces of the gate structure120 a and may be on substantially the same plane. Due to the sidesurfaces structure of the gate structure 120 a, inner side surfaces ofthe spacers 130 a surrounding the side surfaces of the gate structure120 a may have a planar shape without a step.

In the MOSFET device 100 a of the present embodiment, a lower surface ofthe first metal layer 125 a and an inner bottom surface of the highdielectric layer 123 a in contact therewith form a first interface (seeIs1′ of FIG. 7), and a lower surface of the WFC layer 127 a and an uppersurface of the first metal layer 125 a and upper surfaces of theprotruding portions of the high dielectric layer 123 a on both sides ofthe high dielectric layer 123 a in contact with the lower surface of theWFC layer 127 a may form a second interface (see Is2′ of FIG. 7). Thefirst interface Is1′ and the second interface Is2′ will be described inmore detail below in the descriptions of FIG. 7. In addition, the secondinterface Is2′ may be longer than the first interface Is1′ in the firstdirection (the x-direction), which is the length direction of a channel.Accordingly, similar to the MOSFET device 100 of FIG. 1, the MOSFETdevice 100 a of the present embodiment may have a uniform concentrationof the WFC material on the first interface Is1′, and accordingly, theGWR phenomenon may not occur in the gate structure 120 a or may beimproved.

FIG. 7 is a conceptual diagram illustrating diffusion paths of the WFCmaterial in the gate structure 120 a of the MOSFET device of FIG. 6A,which may correspond to a portion of the gate structure 120 a of FIG. 6Aor 6B.

Referring to FIG. 7, in the MOSFET device 100 a of the presentembodiment, the first interface Is1′ may be a lower surface portion ofthe first metal layer 125 a in contact with the inner bottom surface ofthe high dielectric layer 123 a, and the second interface Is2′ may be alower surface portion of the WFC layer 127 a in contact with the uppersurface of the first metal layer 125 a and upper surfaces of theprotruding portions of the high dielectric layer 123 a on both sides ofthe high dielectric layer 123 a.

In FIG. 7, the first interface Is1′ may have a first length L1′ in thefirst direction (the x-direction), and the second interface Is2′ mayhave a second length L2′ in the first direction (the x-direction). Thesecond length L2′ may be greater than the first length L1′, and inaddition, the second interface Is2′ may be longer than the firstinterface Is1′ at both edge portions that are spaced apart from eachother in the first direction (the x-direction).

In view of the diffusion paths of the WFC material of the WFC layer 127a, the WFC material (for example, Al) may move from the second interfaceIs2′ to the first interface Is1′ in the third direction (thez-direction) or the second direction (the y-direction). In addition, asillustrated by small arrows, paths through which the WFC materialdiffuses from the second interface Is2′ to each portion of the firstinterface Is1′ may be substantially the same as each other. Accordingly,in the MOSFET device 100 a of the present embodiment, the concentrationof the WFC material at the center portion of the first interface Is1′may be substantially the same as the concentration of the WFC materialat the edge portion of the first interface Is1′. In other words, theconcentrations of the WFC material on the first interface Is1′ may beuniform along the first direction (the x-direction), and accordingly,the GSW phenomenon may not occur in the gate structure 120 a or may begreatly improved.

In contrast, when a second MOSFET device (also referred to as a secondcomparative MOSFET device) includes layers all similar to layers of gatestructure 120 a except an interface layer have a U-shaped shape, asecond interface may be shorter than a first interface in a firstdirection and paths illustrated by bold arrows among paths through whichthe WFC material in the MOSFET device 100 a of the present embodimentdiffuses from the second interface Is2′ to the edge portion of the firstinterface Is1′, may not exist. As a result, as compared with the firstcomparative MOSFET device, in the second comparative MOSFET device, adifference in concentrations of the WFC material between the edgeportion and the center portion of the first interface Is1 may increase,and the increased difference in concentrations of the WFC material maycause more serious GWR problems.

FIG. 8 is a graph showing work functions of each portion of the gatestructure 120 a of the second comparative MOSFET device and the MOSFETdevice 100 a of FIG. 6A, wherein a solid line represents work functionsof the second comparative MOSFET device, and a dashed line representswork functions of the MOSFET device 100 a of FIG. 6A. The x-axisrepresents a position in the gate structure 120 a, the y-axis representswork functions, and a unit may be an arbitrary unit.

Referring to FIG. 8, regarding the GWR phenomenon, in which a workfunction of a gate edge of the gate structure 120 a is greater than awork function of a gate center of the gate structure 120 a, a differencein work functions between the gate center and the gate edge in thesecond comparative MOSFET device is a first GWR GWR1′, and a differencein work functions between the gate center and the gate edge in theMOSFET device 100 a is a second GWR GWR2′. The first GWR GWR1′ may berelatively large, for example, about several hundreds meV. For example,the second GWR GWR2′ may be, for example, less than 50% of the first GWRGWR1′.

When the work function of the gate center is about 4.5 eV, the first GWRGWR1′ is about 350 meV, and the second GWR GWR2′ is about 150 meV, thefirst GWR GWR1′ may be about 7.8% and the second GWR GWR2′ may be about3.3% of the work function of the gate center. In other words, in theMOSFET device 100 a of the present embodiment, the GWR may be reduced toabout 4/10 as compared to that of the second comparative MOSFET device.In addition, in the MOSFET device 100 a of the present embodiment, theDC performance may be improved by 6% or more as compared to that of thesecond comparative MOSFET device.

Accordingly, the MOSFET device 100 a of the present embodiment mayinclude the second interface Is2′ that is longer than the firstinterface Is1′ in the first direction (the x-direction), which is thelength direction of the channel, such that the concentrations of the WFCmaterial on the first interface Is1′ may be uniform (e.g., uniform alongthe first direction), and the work functions of the gate structure 120 amay be uniform (e.g., uniform along the first direction). Accordingly,the MOSFET device 100 a of the present embodiment greatly reduces theGWR phenomenon of the gate structure 120 a, thereby implementing areliable MOSFET device.

FIGS. 9A to 9D are cross-sectional views of MOSFET devices according tosome embodiments of the inventive concept, which are cross-sectionalviews corresponding to FIG. 2A. Descriptions already given with respectto FIGS. 1 to 2C, 6A, and 6B are briefly given or omitted below.

Referring to FIG. 9A, a MOSFET device 100 b of the present embodimentmay be different from the MOSFET device 100 a of FIG. 6A in that only aWFC layer 127 b has a U-shape. In detail, in the MOSFET device 100 b ofthe present embodiment, an interface layer 121 b, a high dielectriclayer 123 b, and a first metal layer 125 b may have a uniform thickness(e.g., a thickness in the second direction (y-direction)) along thefirst direction (the x-direction). In addition, the WFC layer 127 b mayhave a U-shape covering a lower surface of a second metal layer 129 band both side surfaces of the second metal layer 129 b, which are spacedapart from each other in the first direction (the x-direction). Due tothe U-shape of the WFC layer 127 b, an upper surface of the second metallayer 129 b, upper surfaces of protruding portions on both sides of theWFC layer 127 b, and upper surfaces of spacers 130 b may be onsubstantially the same plane. An inner side surface of each of thespacers 130 b may have a step.

In the MOSFET device 100 b of the present embodiment, a lower surface ofthe first metal layer 125 b and an upper surface of the high dielectriclayer 123 b in contact therewith may form a first interface, and a lowersurface of the WFC layer 127 b may form a second interface. In addition,the second interface may be longer than the first interface in the firstdirection (the x-direction), which is the length direction of a channel.Accordingly, in the MOSFET device 100 b of the present embodiment, theconcentrations of the WFC material on the first interface may be uniform(e.g., uniform along the first direction (the x-direction)), and the GWRphenomenon may not occur in a gate structure 120 b or may be improved.

Referring to FIG. 9B, a MOSFET device 100 c of the present embodimentmay be different from the MOSFET device 100 of FIG. 2A in that a WFClayer 127 c has a U-shape. In detail, in the MOSFET device 100 c of thepresent embodiment, an interface layer 121 c, a high dielectric layer123 c, and a first metal layer 125 c may have a uniform thickness (e.g.,a thickness in the second direction (y-direction)) along the firstdirection (the x-direction), the interface layer 121 c and the highdielectric layer 123 c may have the same length in the first direction(the x-direction), and the first metal layer 125 c may be longer thanthe high dielectric layer 123 c in the first direction (thex-direction). In addition, the WFC layer 127 c may have a U-shapecovering a lower surface of a second metal layer 129 c and both sidesurfaces of the second metal layer 129 c, which are spaced apart fromeach other in the first direction (the x-direction). Due to the U-shapeof the WFC layer 127 c, an upper surface of the second metal layer 129c, upper surfaces of protruding portions of the WFC layer 127 c on bothsides of the WFC layer 127 c, and upper surfaces of the spacers 130 cmay be on substantially the same plane. An inner side surface of each ofthe spacers 130 c may have a step.

In the MOSFET device 100 c of the present embodiment, a lower surface ofthe first metal layer 125 c and an upper surface of the high dielectriclayer 123 c in contact therewith may form a first interface, and a lowersurface of the WFC layer 127 b and an upper surface of the first metallayer 125 c in contact therewith may form a second interface. Inaddition, the second interface may be longer than the first interface inthe first direction (the x-direction), which is the length direction ofa channel. Accordingly, in the MOSFET device 100 c of the presentembodiment, the concentrations of the WFC material on the firstinterface may be uniform (e.g., uniform along the first direction (thex-direction)), and the GWR phenomenon may not occur in a gate structure120 c or may be improved.

Referring to FIG. 9C, a MOSFET device 100 d of the present embodimentmay be different from the MOSFET device 100 a of FIG. 6A in that only ahigh dielectric layer 123 d has a U-shape. In detail, in the MOSFETdevice 100 d of the present embodiment, the high dielectric layer 123 dmay have a U-shape covering a lower surface of a first metal layer 125 dand both side surfaces of the first metal layer 125 d, which are spacedapart from each other in the first direction (the x-direction). Due tothe U-shape of the high dielectric layer 123 d, an upper surface of thefirst metal layer 125 d and upper surfaces of protruding portions of thehigh dielectric layer 123 d on both sides of the high dielectric layer123 d may be on substantially the same plane and may be in contact witha lower surface of a WFC layer 127 d. The WFC layer 127 d and a secondmetal layer 129 d may have a uniform thickness (e.g., a thickness in thesecond direction (y-direction)) along the first direction (thex-direction). An inner side surface of each of spacers 130 d may nothave a step.

In the MOSFET device 100 d of the present embodiment, the lower surfaceof the first metal layer 125 d and an inner bottom surface of the highdielectric layer 123 d in contact therewith may form a first interface,and the lower surface of the WFC layer 127 d and the upper surface ofthe first metal layer 125 d and the upper surfaces of the protrudingportions of the high dielectric layer 123 d on both sides of the highdielectric layer 123 d in contact with the lower surface of the WFClayer 127 d may form a second interface. In addition, the secondinterface may be longer than the first interface in the first direction(the x-direction), which is the length direction of a channel.Accordingly, in the MOSFET device 100 d of the present embodiment, theconcentrations of the WFC material on the first interface may be uniform(e.g., uniform along the first direction (the x-direction)), and the GWRphenomenon may not occur in a gate structure 120 d or may be improved.

Referring to FIG. 9D, a MOSFET device 100 e may be different from theMOSFET device 100 a of FIG. 6A in that a U-shape of a WFC layer 127 e isformed longer than a U-shape of a high dielectric layer 123 e in thefirst direction (the x-direction). In detail, in the MOSFET device 100 eof the present embodiment, the high dielectric layer 123 e may have aU-shape covering a lower surface of a first metal layer 125 e and bothside surfaces of the first metal layer 125 e, which are spaced apartfrom each other in the first direction (the x-direction). Due to theU-shape of the high dielectric layer 123 e, an upper surface of thefirst metal layer 125 e and upper surfaces of protruding portions of thehigh dielectric layer 123 e on both sides of the high dielectric layer123 e may be on substantially the same plane and may be in contact withthe WFC layer 127 e.

In addition, the WFC layer 127 e may have a U-shape covering a lowersurface of a second metal layer 129 e and both side surfaces of thesecond metal layer 129 e, which are spaced apart from each other in thefirst direction (the x-direction). Due to the U-shape of the WFC layer127 e, an upper surface of the second metal layer 129 e, upper surfacesof the protruding portions of the WFC layer 127 e on both sides of theWFC layer 127 e, and upper surfaces of spacers 130 e may be onsubstantially the same plane. However, as shown in FIG. 9D, the lowersurface of the WFC layer 127 e may be longer than the lower surface ofthe high dielectric layer 123 e in the first direction (thex-direction). An inner side surface of each of the spacers 130 e mayhave a step.

In the MOSFET device 100 e of the present embodiment, a lower surface ofthe first metal layer 125 e and an inner bottom surface of the highdielectric layer 123 e in contact therewith may form a first interface,and the lower surface of the WFC layer 127 e may form a secondinterface. In addition, the second interface may be longer than thefirst interface in the first direction (the x-direction), which is thelength direction of a channel. Accordingly, in the MOSFET device 100 eof the present embodiment, the concentrations of the WFC material on thefirst interface may be uniform (e.g., uniform along the first direction(the x-direction)), and the GWR phenomenon may not occur in a gatestructure 120 e or may be improved.

FIGS. 10A and 10B are cross-sectional views of MOSFET devices accordingto some embodiments of the inventive concept, which are cross-sectionalviews corresponding to FIG. 2B. Descriptions already given with respectto FIGS. 1 to 2C, 6A, 6B, and 9A to 9D are briefly given or omittedbelow.

Referring to FIG. 10A, a MOSFET device 100 f of the present embodimentmay be different from the MOSFET device 100 of FIG. 1 in that a secondmetal layer 129 f has a U-shape and further includes a gap-fill layer126 therein. In detail, in the MOSFET device 100 f of the presentembodiment, the second metal layer 129 f may have a U-shape covering alower surface of the gap-fill layer 126 and both side surfaces of thegap-fill layer 126, which are spaced apart from each other in the firstdirection (the x-direction). Due to the U-shape of the second metallayer 129 f, an upper surface of the gap-fill layer 126, upper surfacesof protruding portions of the second metal layer 129 f on both sides ofthe second metal layer 129 f, and upper surfaces of spacers 130 f may beon substantially the same plane.

The gap-fill layer 126 may be arranged on the second metal layer 129 fand may include, for example, tungsten (W). However, a material of thegap-fill layer 126 is not limited to tungsten. The gap-fill layer 126may include various metals suitable for filling a gap. For example, thegap-fill layer 126 may include a material selected from a groupincluding a metal nitride such as TiN, TaN, or the like, Al, a metalcarbide, a metal silicide, a metal aluminum carbide, a metal aluminumnitride, and a metal silicon nitride. For reference, when a gatestructure 120 f is formed in a replacement metal gate (RMG) structure,the gap-fill layer 126 may be a metal layer that finally fills aremaining gap. Accordingly, when the second metal layer 129 f issufficiently thick, the gap-fill layer 126 may be omitted. Each of thespacers 130 f may include a step in an inner side surface thereof.

In the MOSFET device 100 f of the present embodiment, a first interfaceand a second interface may have substantially the same shape as thefirst interface and the second interface of the MOSFET device 100 ofFIG. 1. Accordingly, in the MOSFET device 100 f of the presentembodiment, the concentrations of the WFC material on the firstinterface may be uniform (e.g., uniform along the first direction (thex-direction)), and the GWR phenomenon may not occur in a gate structure120 f or may be improved.

Referring to FIG. 10B, a MOSFET device 100 g of the present embodimentmay be different from the MOSFET device 100 a of FIG. 6A in that asecond metal layer 129 g has a U-shape and further includes the gap-filllayer 126 therein. In detail, in the MOSFET device 100 g of the presentembodiment, the second metal layer 129 g may be arranged in a WFC layer127 g having a U-shape, and may have a U-shape covering a lower surfaceof the gap-fill layer 126 and both side surfaces of the gap-fill layer126, which are spaced apart from each other in the first direction (thex-direction). Due to the U-shape of the WFC layer 127 g and the U-shapeof the second metal layer 129 g, an upper surface of the gap-fill layer126, upper surfaces of protruding portions of the second metal layer 129g on both sides of the second metal layer 129 g, upper surfaces ofprotruding portions of the WFC layer 127 g on both sides of the WFClayer 127 g, and upper surfaces of spacers 130 g may be on substantiallythe same plane. The gap-fill layer 126 is as described as the gap-filllayer 126 in the MOSFET device 100 f of FIG. 10A. Each of the spacers130 g may not have a step in an inner side surface thereof.

In the MOSFET device 100 g of the present embodiment, a first interfaceand a second interface may have substantially the same shape as thefirst interface and the second interface of the MOSFET device 100 a ofFIG. 6A. Accordingly, in the MOSFET device 100 g of the presentembodiment, the concentrations of the WFC material on the firstinterface may be uniform (e.g., uniform along the first direction (thex-direction)), and the GWR phenomenon may not occur in a gate structure120 g or may be improved.

FIGS. 11A and 11B are cross-sectional views of MOSFET devices accordingto some embodiments, which are cross-sectional views corresponding toFIG. 2B. Descriptions already given with respect to FIGS. 1 to 2C, 6A,6B, 9A to 9D, 10A, and 10B are briefly given or omitted below.

Referring to FIG. 11A, a MOSFET device 100 h of the present embodimentmay be different from the MOSFET device 100 of FIG. 1 in that the MOSFETdevice 100 h has a planar structure (e.g., a planar channel region)instead of a fin structure. In detail, the MOSFET device 100 h mayinclude the semiconductor substrate 101, an active area ACTp, and a gatestructure 120 h. The semiconductor substrate 101 and the gate structure120 h are similar to or the same as those described with reference tothe MOSFET device 100 of FIG. 1. However, the semiconductor substrate101 and the gate structure 120 h may be different from the semiconductorsubstrate 101 and the gate structure 120 of the MOSFET device 100 ofFIG. 1 in that no fin is formed on the semiconductor substrate 101, andthus, the gate structure 120 h does not cover the fin.

The active area ACTp may be defined by a device isolation film and mayextend on the semiconductor substrate 101 in the first direction (thex-direction). The gate structure 120 h may cross the active area ACTp onthe semiconductor substrate 101 and extend in the second direction (they-direction). The active area ACTp may include an impurity area formedby injecting impurity ions into the semiconductor substrate 101 at ahigh concentration. For example, the active area ACTp may includesource/drain areas 103 p formed by injecting impurity ions at a highconcentration into an upper area of the semiconductor substrate 101 onboth sides of the gate structure 120 h, and a channel area 105 p belowthe gate structure 120 h. Each of the source/drain areas 103 p mayinclude a high concentration doped area 103 h and a low concentrationdoped area 1031.

In the MOSFET device 100 h of the present embodiment, the gate structure120 h may have a planar structure in which internal layers have auniform thickness (e.g., a uniform thickness in the third direction(z-direction) along the first direction (the x-direction)) and aresequentially stacked in the third direction (the z-direction). As shownin FIG. 11A, a vertical cross-sectional structure of the gate structure120 h may be substantially the same as a cross-sectional structure ofthe gate structure 120 of the MOSFET device 100 of FIG. 2B. Accordingly,like the first interface and the second interface of the MOSFET device100 of FIG. 1, in a first interface and a second interface of the MOSFETdevice 100 h of the present embodiment, the second interface may belonger than the first interface in the first direction (thex-direction). As a result, in the MOSFET device 100 h of the presentembodiment, the concentrations of the WFC material on the firstinterface may be uniform (e.g., uniform along the first direction (thex-direction)), and the GWR phenomenon may not occur in a gate structure120 h or may be improved. Each of spacers 130 h may have a step in aninner side surface thereof.

Referring to FIG. 11B, a MOSFET device 100 i may be different from theMOSFET device 100 a of FIG. 6 in that the MOSFET device 100 i has aplanar structure instead of a fin structure. In detail, the MOSFETdevice 100 i of the present embodiment may include the semiconductorsubstrate 101, the active area ACTp, and a gate structure 120 i. Thesemiconductor substrate 101, the active area ACTp, and the gatestructure 120 i are as described in the MOSFET device 100 of FIG. 6A andthe MOSFET device 100 h of FIG. 11A.

In the MOSFET device 100 i of the present embodiment, the gate structure120 i may have a planar structure in which internal layers have auniform thickness (e.g., a uniform thickness in the third direction(z-direction) along the first direction (the x-direction)) and aresequentially stacked in the third direction (the z-direction). As shownin FIG. 11B, a vertical cross-sectional structure of the gate structure120 i may be substantially the same as a cross-sectional structure ofthe gate structure 120 a of the MOSFET device 100 a of FIG. 6A.Accordingly, like the first interface and the second interface of theMOSFET device 100 a of FIG. 6A, in a first interface and a secondinterface of the MOSFET device 100 i of the present embodiment, thefirst interface may be longer than the second interface in the firstdirection (the x-direction). As a result, in the MOSFET device 100 i ofthe present embodiment, the concentrations of the WFC material on thefirst interface may be uniform (e.g., uniform along the first direction(the x-direction)), and the GWR phenomenon may not occur in the gatestructure 120 i or may be improved. Each of spacers 130 i may not have astep in an inner side surface thereof.

MOSFET devices of various structures have been described. However, theinventive concept is not limited to the structures of the MOSFET devicesdescribed herein. For example, the inventive concept may extend to allMOSFET devices including a gate structure in which a second interface islonger than a first interface in a length direction of a channel.

FIGS. 12A to 12H are cross-sectional views schematically illustratingmethods of manufacturing the MOSFET device 100 of FIG. 1, according tosome embodiments of the inventive concept. It will be described belowwith reference to FIGS. 1 to 2C, and descriptions already given withrespect to FIGS. 1 to 2C are briefly given or omitted below.

Referring to FIG. 12A, in methods of manufacturing a MOSFET device ofthe present embodiment, first, an upper portion of the semiconductorsubstrate 101 is etched to form the fin 105 having a structureprotruding from the semiconductor substrate 101. The fin 105 may beformed in a structure extending in the first direction (the x-direction)on the semiconductor substrate 101. The fin 105 may include the lowerfin portion 105 d and the upper fin portion 105 u.

Referring to FIG. 12B, after forming the fin 105, the device isolationfilm 110 (e.g., the device isolation film 110 in FIG. 2C) covering alower portion of both opposing side surfaces of the fin 105 is formed.The opposing side surfaces of the lower fin portion 105 d of the fin 105are spaced apart from each other in the second direction (they-direction). After forming the device isolation film 110, only theupper fin portion 105 u of the fin 105 may have a structure protrudingfrom the device isolation film 110.

After the device isolation film 110 is formed, a dummy gate structure120 du including a dummy insulating film 121 du and a dummy gateelectrode 123 du is formed, and the spacers 130 are formed on both sidesurfaces of the dummy gate structure 120 du. The dummy gate structure120 du and the spacers 130 may be formed in, for example, a structureextending in the second direction (the y-direction) while covering aportion of the fin 105. In detail, the dummy gate structure 120 du andthe spacers 130 may have a structure surrounding an upper surface andside surface portions of the upper fin portion 105 u of the fin 105 onthe device isolation film 110 as illustrated in FIG. 2C.

Referring to FIG. 12C, portions of the upper fin portion 105 uprotruding above the device isolation film 110, which are adjacent sidesurfaces of the dummy gate structure 120 du are removed, and thesource/drain areas 103 are formed on the lower fin portion 105 d bygrowing an epitaxial film. The source/drain areas 103 may include, forexample, at least one of SiGe, Ge, Si, and SiC epitaxially grown on thelower fin portion 105 d.

As shown in FIG. 12C, upper surfaces of the source/drain areas 103 maybe higher than an upper surface of the upper fin portion 105 u below thedummy gate structure 120 du. In addition, the source/drain areas 103 maycover a lower portion of the spacers 130. In some embodiments, the upperfin portion 105 u may not be removed, and the source/drain areas 103 maybe formed on the upper fin portion 105 u. In this case, the source/drainareas 103 may maintain an initial shape of the upper fin portion 105 u,or may be formed on the upper fin portion 105 u through epitaxial growthto have a different shape from the initial shape of the upper finportion 105 u.

Referring to FIG. 12D, after the source/drain areas 103 are formed, aninsulating film covering resultants on the substrate 101 is formed andplanarized to form an interlayer insulating film (not shown). After theinterlayer insulating film is formed, the dummy gate structure 120 du isremoved. In the removal of the dummy gate structure 120 du, only thedummy gate electrode 123 du may be removed, or the dummy insulating film121 du may be removed together. When the dummy insulating film 121 du(e.g., a portion of the dummy insulating film 121 du) remains, the dummyinsulating film 121 du may be used as the interface layer 121.

Then, the high dielectric layer 123 is formed on the interface layer 121between two spacers 130. The high dielectric layer 123 is formed throughan anisotropic deposition method in which the high dielectric layer 123is not deposited on an inner side surface of the two spacers 130 but isdeposited only on an upper surface of a layer therebelow. Accordingly,the high dielectric layer 123 may have a uniform thickness in the thirddirection (z-direction) along the first direction (the x-direction).When the dummy insulating film 121 du is also removed from the dummygate structure 120 du, before forming the high dielectric layer 123, theinterface layer 121 may be separately formed through the anisotropicdeposition method.

Referring to FIG. 12E, inner side surfaces of the two spacers 130, whichare adjacent to each other, are etched to increase a distance betweenthe two spacers 130 in the first direction (the x-direction). Anoperation of etching the inner side surfaces of the two spacers 130 maybe an operation of securing a space for the first metal layer 125, theWFC layer 127, and the second metal layer 129, which have a longerlength than the high dielectric layer 123 in the first direction (thex-direction).

The etching of the inner side surfaces of the two spacers 130 may beperformed, for example, through an etchback operation. The etching ofthe inner side surfaces of the two spacers 130 is not limited to theetchback operation. During the etching of the inner side surfaces of thetwo spacers 130, a portion of an upper portion of the two spacers 130may be removed. In some embodiments, a portion of the high dielectriclayer 123 may also be removed.

Referring to FIG. 12F, after etching the inner side surfaces of the twospacers 130, the first metal layer 125 is formed on the high dielectriclayer 123 between the two spacers 130. The first metal layer 125 may beformed through the anisotropic deposition method in which the firstmetal layer 125 is not deposited on the inner side surfaces of the twospacers 130 but is only deposited on the high dielectric layer 123. Evenwhen the anisotropic deposition method is performed, the first metallayer 125 may be deposited on inner bottom surfaces of the two spacer130 s. Accordingly, as shown in FIG. 12F, the first metal layer 125 maybe longer than the high dielectric layer 123 in the first direction (thex-direction).

Referring to FIGS. 12G and 12H together, subsequently, the WFC layer 127is formed on the first metal layer 125 between the two spacers 130adjacent to each other. The WFC layer 127 may be formed through theanisotropic deposition method in which the WFC layer 127 is notdeposited on the inner side surfaces of the two spacers 130 but is onlydeposited on the first metal layer 125.

After the WFC layer 127 is formed, the second metal layer 129 is formedon the WFC layer 127. The second metal layer 129 may be formed throughthe anisotropic deposition method or may be formed through an isotropicor conformal deposition method. When the second metal layer 129 isformed through the conformal deposition method, after depositing a metalmaterial forming the second metal layer 129, the second metal layer 129may be formed through a planarization operation exposing the uppersurfaces of the two spacers 130.

The MOSFET device 100 of FIG. 1 may be completed through the formationof the second metal layer 129. In the manufacturing method of the MOSFETdevice of the present embodiment, the MOSFET device 100 of FIG. 1, inwhich the second interface is longer than the first interface in thefirst direction (the x-direction), may be easily manufactured byperforming an operation of increasing a distance between inner sidesurfaces of the two spacers 130 in the first direction (the x-direction)and then forming the first metal layer 125 and the WFC layer 127 throughthe anisotropic deposition method.

FIGS. 13A and 13B are cross-sectional views schematically illustrating amanufacturing operation of the MOSFET device 100 of FIG. 1, according tosome embodiments. It will be described below with reference to FIGS. 1to 2C, and descriptions already given with respect to FIGS. 12A to 12Hare briefly given or omitted below.

Referring to FIG. 13A, in a manufacturing method of the MOSFET device ofthe present embodiment, first, the dummy gate structure 120 du isremoved, and then the high dielectric layer 123 is formed on theinterface layer 121, through the operations of FIGS. 12A to 12D. In themanufacturing method of the MOSFET device of the present embodiment, thehigh dielectric layer 123 may be formed to have a uniform thickness onthe upper surface of the interface layer 121 and the inner side surfacesof the two spacers 130 through the conformal deposition method insteadof the anisotropic deposition method.

Referring to FIG. 13B, the inner side surfaces of the two spacers 130which are adjacent to each other are etched to increase the distancebetween the two spacers 130 in the first direction (the x-direction). Inthe operation of etching the inner side surfaces of the two spacers 130,a portion of the high dielectric layer 123 on the inner side surfaces ofthe two spacers 130 may also be removed together. As a result, after theoperation of etching the inner side surfaces of the two spacers 130, astructure substantially the same as the structure of FIG. 12E may beformed. Then, the MOSFET device 100 of FIG. 1 may be completed throughoperations of FIGS. 12F to 12H.

FIGS. 14A to 14E are cross-sectional views schematically illustratingmethods of manufacturing the MOSFET device 100 a of FIG. 6A, accordingto some embodiments of the inventive concept, which are cross-sectionalviews corresponding to FIG. 6B. It will be described below withreference to FIGS. 6A and 6B, and descriptions already given withrespect to FIGS. 12A to 13B are briefly given or omitted below.

Referring to FIG. 14A, in a manufacturing method of the MOSFET device ofthe present embodiment, first, the dummy gate structure 120 du isremoved, and the high dielectric layer 123 a is formed on the interfacelayer 121 a, through the operations of FIGS. 12A to 12D. The highdielectric layer 123 a may be formed to have a uniform thickness on theupper surface of the interface layer 121 a and the inner side surfacesof two spacers 130 a through the conformal deposition method instead ofthe anisotropic deposition method. In some embodiments, the highdielectric layer 123 a may have a first thickness on the upper surfaceof the interface layer 121 a and may have a second thickness on theinner side surfaces of two spacers 130 a as illustrated in FIG. 14A.

Referring to FIG. 14B, the first metal layer 125 a is formed on the highdielectric layer 123 a. The first metal layer 125 a may be formed tohave a uniform thickness on the upper surface and inner side surfaces ofthe high dielectric layer 123 a through the conformal deposition methodinstead of the anisotropic deposition method.

Referring to FIG. 14C, protruding portions of the high dielectric layer123 a and the first metal layer 125 a are removed. Through the removalof the protruding portions, the high dielectric layer 123 a may end uphaving a U-shape, and the first metal layer 125 a may be maintained onlyin the U-shape of the high dielectric layer 123 a. Accordingly, the highdielectric layer 123 a may surround the lower surface and side surfacesof the first metal layer 125 a, and the upper surface of the first metallayer 125 a may be on substantially the same plane as the upper surfacesof the protruding portions of the high dielectric layer 123 a.

Referring to FIG. 14D, the WFC layer 127 a is formed on the first metallayer 125 a. The WFC layer 127 a may be formed to have a uniformthickness on the upper surface of the first metal layer 125 a, the uppersurfaces of the protruding portions of the high dielectric layer 123 a,and the inner side surfaces of the two spacers 130 through the conformaldeposition method instead of the anisotropic deposition method.

Referring to FIG. 14E, after the WFC layer 127 a is formed, the secondmetal layer 129 a is formed on the WFC layer 127 a. The second metallayer 129 a may be formed through the conformal deposition method.Accordingly, after depositing a metal material forming the second metallayer 129 a, the second metal layer 129 a may be formed through aplanarization operation exposing the upper surfaces of the two spacers130 a.

The MOSFET device 100 a of FIG. 6A may be completed through theformation of the second metal layer 129 a. In the manufacturing methodof the MOSFET device of the present embodiment, the MOSFET device 100 aof FIG. 6A, in which the second interface is longer than the firstinterface in the first direction (the x-direction), may be easilymanufactured by not performing a separate operation of increasing thedistance between the inner side surfaces of the two spacers 130 a andforming the high dielectric layer 123 a, the first metal layer 125 a,and the WFC layer 127 a through the conformal deposition method, theremoval of the protruding portions, or the like.

FIGS. 15A and 15B are cross-sectional views schematically illustratingmethods of manufacturing the MOSFET device 100 e of FIG. 9D, accordingto some embodiments of the inventive concept, which are cross-sectionalviews corresponding to FIG. 2B. It will be described below withreference to FIG. 9D, and descriptions already given with respect toFIGS. 12A to 14E are briefly given or omitted below.

Referring to FIG. 15A, in a manufacturing method of the MOSFET device ofthe present embodiment, the dummy gate structure 120 du is removedthrough the operations of FIGS. 12A to 12D. Then, as in the operationsof FIGS. 14A and 14B, the high dielectric layer 123 e and the firstmetal layer 125 e are formed on the interface layer 121 e. The highdielectric layer 123 e may be formed to have a uniform thickness on theupper surface of the interface layer 121 e and the inner side surfacesof the two spacers 130 e through the conformal deposition method, and inaddition, the first metal layer 125 e may be formed to have a uniformthickness on the upper surface and the inner side surfaces of the highdielectric layer 123 e through the conformal deposition method.

Subsequently, the inner side surfaces of the two spacers 130 e which areadjacent to each other are etched to increase the distance between thetwo spacers 130 e in the first direction (the x-direction). In anoperation of etching the inner side surfaces of the two spacers 130 e, aportion of the high dielectric layer 123 e and the first metal layer 125e on the inner side surfaces of the two spacers 130 e may be removedtogether. In addition, the high dielectric layer 123 e may become aU-shape, and the first metal layer 125 e may be maintained only insidethe U-shape of the high dielectric layer 123 e.

Referring to FIG. 15B, the WFC layer 127 e is formed on the first metallayer 125 e. The WFC layer 127 e may be formed to have a uniformthickness on the upper surface of the first metal layer 125 e, the uppersurfaces of the protruding portions of the high dielectric layer 123 e,and inner bottom surfaces and the side surfaces of the two spacer 130 ethrough the conformal disposition method.

After the WFC layer 127 e is formed, the second metal layer 129 e isformed on the WFC layer 127 e. The second metal layer 129 e may beformed through the conformal deposition method. Accordingly, afterdepositing a metal material forming the second metal layer 129 e, thesecond metal layer 129 e may be formed through the planarizationoperation exposing the upper surfaces of the two spacers 130 e.

The MOSFET device 100 e of FIG. 9D may be completed through theformation of the second metal layer 129 e. In the manufacturing methodof the MOSFET device of the present embodiment, the MOSFET device 100 eof FIG. 9D, in which the second interface is longer than the firstinterface in the first direction (the x-direction), may be easilymanufactured by performing the operation of removing the inner sidesurfaces of the two spacers 130 to increase the distance between theinner side surfaces of the two spacers 130 e after the first metal layer125 e is formed, and forming the high dielectric layer 123 e, the firstmetal layer 125 e, and the WFC layer 127 e through the conformaldeposition method.

Although not described in detail, the MOSFET devices 100 b, 100 c, and100 d of FIGS. 9A to 9C may be easily manufactured by appropriatelycombining the anisotropic deposition or conformal deposition, theremoving of the inner side surfaces of spacers, the removing ofprotruding portions of a layer, or the like.

While the inventive concept has been particularly shown and describedwith reference to example embodiments thereof, it will be understoodthat various changes in form and details may be made therein withoutdeparting from the scope of the following claims.

1. A metal oxide field-effect transistor (MOSFET) device comprising: a semiconductor substrate; an active area on the semiconductor substrate and extending in a first direction; and a gate structure on the semiconductor substrate, the gate structure extending across the active area in a second direction that traverses the first direction and comprising an interface layer, a high-k layer, a first metal layer, a work function control (WFC) layer, and a second metal layer, which are sequentially stacked on the active area, and each of the high-k layer, the first metal layer, the WFC layer, and the second metal layer comprising a lower surface facing the semiconductor substrate and an upper surface opposite the lower surface, wherein the lower surface of the WFC layer is longer than a first interface between the lower surface of the first metal layer and the upper surface of the high-k layer in the first direction.
 2. (canceled)
 3. The MOSFET device of claim 1, wherein the WFC layer comprises a WFC material, and a concentration of the WFC material on the first interface is uniform along the first direction.
 4. The MOSFET device of claim 1, wherein each of the high-k layer, the first metal layer, and the WFC layer has a uniform thickness along the first direction, the high-k layer is shorter than the first metal layer in the first direction, and lengths of the first metal layer and the WFC layer in the first direction are substantially equal to each other.
 5. The MOSFET device of claim 4, wherein the active area comprises a fin structure protruding from the semiconductor substrate, and the fin structure comprises side surfaces that are spaced apart from each other in the second direction, the gate structure extends on an upper surface of the fin structure and both the side surfaces of the fin structure, and the gate structure comprises side surfaces that are spaced apart from each other in the first direction, spacers are respectively on the side surfaces of the gate structure, and inner side surfaces of the spacers have respective steps adjacent the first interface.
 6. The MOSFET device of claim 1, wherein each of the first metal layer and the second metal layer comprises side surfaces that are spaced apart from each other in the first direction, the high-k layer comprises a bottom portion extending on the lower surface of the first metal layer and protruding portions extending respectively on the side surfaces of the first metal layer, the WFC layer comprises a bottom portion extending on the lower surface of the second metal layer and protruding portions extending respectively on the side surfaces of the second metal layer, and the lower surface of the WFC layer is in contact with the upper surface of the first metal layer and upper surfaces of the protruding portions of the high-k layer.
 7. The MOSFET device of claim 6, wherein the active area comprises a fin structure protruding from the semiconductor substrate, and the fin structure comprises side surfaces that are spaced apart from each other in the second direction, the gate structure extends on an upper surface of the fin structure and both the side surfaces of the fin structure, and the gate structure comprises side surfaces that are spaced apart from each other in the first direction, spacers are respectively on the side surfaces of the gate structure, and side surfaces of the interface layer, the high-k layer, and the WFC layer are coplanar with each other and are in contact with inner side surfaces of the spacers.
 8. The MOSFET device of claim 1, wherein the WFC layer comprises aluminum (Al).
 9. (canceled)
 10. The MOSFET device of claim 1, wherein lengths of the first metal layer and the WFC layer are substantially equal to each other in the first direction, and the lower surface of the WFC layer forms a second interface with the upper surface of the first metal layer, and the second interface is longer than the first interface in the first direction.
 11. The MOSFET device of claim 1, wherein the gate structure comprises side surfaces that are spaced apart from each other in the first direction, and the MOSFET device further comprises spacers that are respectively on the side surfaces of the gate structure, inner side surfaces of the spacers each have a step or a planar shape adjacent the first interface.
 12. A metal oxide field-effect transistor (MOSFET) device comprising: a semiconductor substrate; an active area protruding from the semiconductor substrate and extending in a first direction; a gate structure on the semiconductor substrate, the gate structure extending in a second direction that traverses the first direction and covering at least a portion of the active area, the gate structure comprising an interface layer, a high-k layer, a first metal layer, a work function control (WFC) layer, and a second metal layer, which are sequentially stacked on the active area, and each of the high-k layer, the first metal layer, the work function control (WFC) layer, and the second metal layer comprising a lower surface facing the semiconductor substrate and an upper surface opposite the lower surface; and source and drain areas respectively on side surfaces of the gate structure, the side surfaces of the gate structure being spaced apart from each other in the first direction, wherein the lower surface of the WFC layer is longer than a first interface between the lower surface of the first metal layer and the upper surface of the high-k layer in the first direction.
 13. (canceled)
 14. The MOSFET device of claim 12, wherein each of the high-k layer, the first metal layer, and the WFC layer has a uniform thickness along the first direction, the high-k layer is shorter than the first metal layer in the first direction, lengths of the first metal layer and the WFC layer are substantially equal to each other in the first direction, and the lower surface of the WFC layer forms a second interface with the upper surface of the first metal layer, and the second interface is longer than the first interface in the first direction.
 15. The MOSFET device of claim 12, wherein each of the first metal layer and the second metal layer comprises side surfaces that are spaced apart from each other in the first direction, the high-k layer has a U-shape and covers the lower surface of the first metal layer and both the side surfaces of the first metal layer, the WFC layer has a U-shape and covers the lower surface of the second metal layer and both the side surfaces of the second metal layer, the lower surface of the WFC layer forms a second interface with the upper surface of the first metal layer and uppermost surfaces of the high-k layer, and the second interface is longer than the first direction in the first direction.
 16. The MOSFET device of claim 12, further comprising spacers that are respectively on the side surfaces of the gate structure, wherein inner side surfaces of the spacers each have a step or a planar shape adjacent the first interface.
 17. The MOSFET device of claim 12, wherein the WFC layer comprises titanium aluminum carbide (TiAlC), and each of the first metal layer and the second metal layer comprises titanium nitride (TiN). 18-25. (canceled)
 26. A metal oxide field-effect transistor (MOSFET) device comprising: a substrate; an active area on the substrate; a gate structure on the active area, the gate structure comprising a high-k layer, a first metal layer, a work function control (WFC) layer, and a second metal layer that are sequentially stacked on the active area, and each of the high-k layer, the first metal layer, the WFC layer, and the second metal layer comprising a lower surface facing the active area and an upper surface opposite the lower surface; and source/drain regions respectively adjacent side surfaces of the gate structure, wherein the lower surface of the WFC layer protrudes outwardly beyond opposing ends of an interface between the lower surface of the first metal layer and the upper surface of the high-k layer.
 27. The MOSFET device of claim 26, wherein the side surfaces of the gate structure are spaced apart from each other in a first direction, and portions of the lower surface of the WFC layer that protrude beyond the respective opposing ends of the interface have an equal length in the first direction.
 28. The MOSFET device of claim 27, wherein the WFC layer comprises a WFC material, and a concentration of the WFC material on the interface is uniform along the first direction.
 29. The MOSFET device of claim 26, wherein the side surfaces of the gate structure are spaced apart from each other in a first direction, and the high-k layer, the first metal layer, the WFC layer, and the second metal layer are stacked in a second direction, and the first metal layer has a thickness in the second direction, and the thickness is uniform along the first direction.
 30. The MOSFET device of claim 26, wherein the side surfaces of the gate structure comprise side surfaces of the high-k layer, side surfaces of the first metal layer, and side surfaces of the WFC layer, the side surfaces of the first metal layer are coplanar with the side surfaces of the WFC layer, respectively, and the side surfaces of the high-k layer are recessed inwardly relative to the side surfaces of the first metal layer, respectively.
 31. The MOSFET device of claim 26, wherein the high-k layer comprises a bottom portion that extends on the lower surface of the first metal layer and protruding portions that protrude respectively from end portions of the bottom portion toward the WFC layer and contact the lower surface of the WFC layer, the bottom portion and the protruding portions of the high-k layer define a space, and the first metal layer is in the space, and the side surfaces of the high-k layer are coplanar with the side surfaces of the WFC layer, respectively. 